In recent years, a two-dimensional image display device (laser display device) capable of representing bright colors has attracted attention. This device adopts three coherent light sources of red, green, and blue (e.g., laser light sources), and has a construction as shown in FIG. 13.
In FIG. 13, reference numeral 600 denotes a two-dimensional image display device using conventional laser light sources. The two-dimensional image display device 600 comprises red, green, and blue laser light sources 601a, 601b, and 601c, beam expanders 602a, 602b, and 602c, light integrators 603a, 603b, and 603c, mirrors 604a and 604c, diffusion plates 606a, 606b, and 606c, diffusion plate wobbling means 605a, 605b, and 605c, spatial light modulation elements 607a, 607b, and 607c, field lenses 608a, 608b, and 608c, a dichroic prism 609, and a projection lens 610.
In the two-dimensional image display device 600, lights emitted from the red, green, and blue laser light sources 601a, 601b, and 601c are expanded by the beam expanders 602a, 602b, and 602c, and pass through the light integrators 603a, 603b, and 603c, respectively. The optical paths of the red and blue lights that pass through the light integrators 603a and 603c are bent at 90° by the mirrors 604a and 604c, respectively, while the optical path of the green light that passes through the light integrator 603b is not bent, and the respective lights irradiate the spatial light modulation elements 607a, 607b, and 607c through the field lenses 608a, 608b, and 608c, and the diffusion plates 606a, 606b, and 606c, respectively. The lights emitted from the three kinds of laser light sources 601a, 601b, and 601c pass through the light integrators 603a, 603b, and 603c, respectively, whereby the illumination distributions on the spatial light modulation elements 607a, 607b, and 607c are made uniform. The lights which are individually modulated by the spatial light modulation elements 607a, 607b, and 607c are multiplexed by the dichroic prism 609 to be coaxial beams that propagate in the same optical path, and further, enlarged and projected by the projection lens 610 to be focused on the screen 61. At this time, since the laser light interference is high, speckle noises are superposed on the image projected on the screen 61. In order to avoid the speckle noises, the diffusion plates 606a, 606b, and 606c are wobbled by the diffusion plate wobbling means 605a, 605b, and 605c, respectively, whereby the speckle noises are temporally averaged.
In the conventional two-dimensional image display device 600 shown in FIG. 13, however, in order to expand the lights from the three kinds of laser light sources 601a˜601c and make the intensity distributions of the lights uniform, three beam expanders and three light integrators are needed. Further, in order to convert the lights from the three kinds of laser light sources into coaxial beams which are parallel to each other and propagate in the same optical path, a lot of lenses and mirrors must be disposed in the device. Consequently, the conventional two-dimensional image display device is undesirably increased in scale.
In order to solve this problem, the optical system of the two-dimensional image display device may be constituted such that, as shown in FIG. 14, initially lights emitted from laser light sources corresponding to three colors of red, green, and blue are mixed using dichroic mirrors, and thereafter, the mixed light is transmitted through a beam expander and a light integrator.
In FIG. 14, reference numeral 700 denotes a conventional two-dimensional display device using laser light sources. The two-dimensional image display device 700 comprises red, green, and blue laser light sources 701a, 701b, and 701c, collimator lenses 704a, 704b, and 704c, first and second dichroic mirrors 705a and 705b, a beam expander 702, a light integrator 703, a projection lens 10, and a liquid crystal panel 71.
The dichroic mirror is obtained by laminating multiple films on a glass substrate, and varies the transmissivity in accordance with the wavelength. In the two-dimensional image display device 700 shown in FIG. 15, the first dichroic mirror 705a reflects lights of wavelengths shorter than a threshold wavelength of about 580 nm, and passes only lights having wavelengths longer than this threshold wavelength. The second dichroic mirror 705b reflects lights of wavelengths shorter than a threshold wavelength of about 490 nm, and passes only lights having wavelengths longer than this threshold wavelength.
In the conventional two-dimensional image display device 700 using the laser light sources, initially, lights emitted from the red, green, and blue laser light sources 701a, 701b, and 701c are collimated by the collimator lenses 704a, 704b, and 704c, respectively, and the collimated lights are converted to coaxial beams that are parallel to each other and propagate through the same optical path, by the first and second dichroic mirrors 705a and 705b, and thereafter, the coaxial beams are applied to the beam expander 702. The light beams incident on the beam expander 702 are expanded by the beam expander 702 and then pass through the light integrator 703. The light integrator 703 includes two fly-eye lenses 703a and 703b each comprising rectangle element lenses being two-dimensionally arrayed, and a collimator lens 703c. The lights incident on the respective element lenses of the first fly-eye lens 703 are focused on the two-dimensional spatial light modulation element by the second fly-eye lens 703b, whereby the light intensity distributions on the respective element lenses are multiplexed on the two-dimensional spatial light modulation element, and consequently, the light intensity distribution on the two-dimensional spatial light modulation element becomes uniform.
The light that passes through the light integrator 703 and thereby has the uniform intensity distribution is focused on the liquid crystal panel 71 by the projection lens 710 (refer to Japanese Published Patent Application No. 10-293268 (Patent Document 1)).